Comparative in vitro activities of cefpiramide and apalcillin against anaerobic bacteria.

The in vitro activities of two new antimicrobial agents, apalcillin and cefpiramide (SM-1652), were evaluated against 324 strains of anaerobic bacteria. Apalcillin (a penicillin derivative) and cefpiramide (a semisynthetic cephalosporin) were compared with piperacillin, moxalactam, and cefoxitin. Organisms studied included the Bacteroides fragilis group, other Bacteroides species, fusobacteria, clostridia, nonsporeforming gram-positive rods, and anaerobic cocci. Piperacillin was found to be the most active overall, inhibiting 96% of the strains tested at its achievable level in serum (128 micrograms/ml). Apalcillin was comparable in activity to piperacillin, inhibiting 93% of anaerobes tested at this concentration. The other antibiotics inhibited ca. 80% of the strains at 32 micrograms/ml. In terms of activities against particular species, apalcillin was active against 75% of B. fragilis group strains and 97 to 100% of all other anaerobes. Cefpiramide inhibited 37% of B. fragilis group strains at 32 micrograms/ml and 68% at 64 micrograms/ml (a level that may be achievable with this drug). Cefpiramide inhibited 92% of all other anaerobes at 32 micrograms/ml and 95% at 64 micrograms/ml. The clostridia other than Clostridium perfringens were the most resistant (84% inhibited at 32 micrograms/ml and 95% inhibited at 64 micrograms/ml).